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As we have learned with the kinetic theory of matter all particles are in constant random motion. So whether matter is in the solid, liquid, or gas state the particles making up the matter are constantly moving. This motion is due to the particles kinetic energy. We have also learned that we can measure the average kinetic energy by measuring the temperature of the substance. Temperature tells us how fast the particles are moving.

We have also learned that all matter has a mass. Mass is thus a measure of the amount of matter present. Density is a measure of the mass divided by the volume. In other words density is a measure of the amount of mass in a given volume, or the number of particle in a given volume.

Let's look at the density of water at different temperatures, hot and cold. The density of water at 25 ° C is 1 g/ml. This is telling us that there are 1 gram of particles in a 1ml volume. If we keep the volume the same and increase the temperature (by adding heat), we are increasing the speed of our particles. By increasing the speed of our particles there are more collisions and thus more space is necessary. In order to have the necessary space for these faster moving particles to move there must be less particles. If we decrease the number of particles then the mass must also decrease. According to the density equation a decrease in mass with a constant volume will decrease the density of our substance. The opposite will occur when decreasing the temperature of our substance.

There are three states of matter solid, liquid, and gas. As we have seen each state of matter has a certain number of particles with a certain degree of order. All particles are in constant random motion and there is an attractive force between these particles. These two things determine the order of the particle and thus whether the matter is in the gas, liquid, or solid state. Let's compare 25ml of a gas, liquid and a solid. In 25 ml of a gas the average kinetic energy or speed of the particles is much greater than the attraction between the particles. This allows the gas to expand and fill its container with a relatively small of particles. The particles are in total disorder and are far apart. This means there a very few number of particles in our 25 ml of gas. In 25 ml of a liquid the particles have more order but are still in disorder. They are also closer together than in a gas and thus, the particles are moving slower (have less kinetic energy). Because of the speed of the particles and there arrangement we will have more particles in 25 ml of a liquid than in 25 ml of a gas. In 25 ml of a solid the particles are in an ordered arrangement and close together. These particles are moving even slower than that of a liquid (low kinetic energy). Here we will have more particles in 25 ml than in either the gas or liquid.

In order to change from one state of matter to another energy must be added or removed because of the difference in the average kinetic energy of the particles in each form of matter. To go from a solid to a liquid heat must be added in order to increase the kinetic energy of the particles and vica-versa. For example, NaCl, which is a solid at room temperature, melts (goes from solid to liquid) at 804 ° C and boils (goes from liquid to a gas) at 1465 ° C. Conversely, N₂O, which is a gas at room temperature, liquefies at -88.5 ° C and solidifies (freezing point) at -102.4 ° C.

Image slowly warming a piece of ice, originally at -25 ° C. as heat energy is added, the temperature of the ice increases (increasing speed of particles), but the ice does not change its physical appearance. A 0° C, however, if we continue to supply heat, the ice begins to melt and liquid water appears. The ice continues to melt, but the temperature stays at a constant 0° C until all the ice is gone. During this and other phase changes, adding or removing heat does not raise the temperature of the system. It just changes the physical state of the substance. In the case of melting ice, the heat energy is used to break or disrupt the intermolecular forces that hold the ice crystal together. We are adding energy to over come the attractive forces present between the particles. The following is a graph of the phase changes of water. (Chemistry, pg. 213)

 Make-up Questions

The process of dissolving occurs at a specific rate. This rate can be effected by three things; temperature of the solvent, agitation, and particle size. By increasing or decreasing all or one of these variables will either increase or decrease how fast a substance will dissolve in another.

Let's look at particle size and how it effects the rate of dissolution. If we were to take a piece of rock salt and the same mass of regular table salt and dissolve them in a given volume of water, which do you think will dissolve faster? On page 5 of your packet you need to create a design table to test this. You also need to include some procedures.

After doing the experiment we discover that the regular table salt will dissolve faster than the rock salt. Why? As the particle size decreases then the surface area of the substance increases, thus allowing for more contact between the water molecules and the salt molecules. Don't forget to do your conclusions on page 5.

Now let's look at how agitation will effect the rate of dissolution. If we were to take the same mass of regular table salt in two different containers and dissolve them in a given volume of water, and then shake one and not the other. Which will dissolve faster? To test this design an experimental design table and include procedures on page 6 of your packet.

After doing the experiment we find that the one we agitated (shook) dissolved faster. Why? As we agitate the mixture the more particles are coming in contact with the water molecules thus causing them to dissolve faster. The one not agitated could only allow a limited number of particles to come in contact with the water molecules thus the process takes longer.

How will temperature effect the rate of dissolution? Using the same mass of regular table salt in two different containers with a given volume of water we will change the water's temperature. By making one temperature hot and one cold, which will dissolve faster? Make sure to create a design table and procedures on page 6 of your packet. Don't forget to keep as many things constant as possible.

By following your procedures we find that the hot water will dissolve faster. Why? Thinking back to the kinetic theory of matter, if we increase the temperature of a substance what happens to the speed of the particles? The speed of our particles will also increase. If our water molecules are moving faster than this allows for more of them to come in contact with our salt particles in a shorter time period thus, increasing the rate of dissolution.

Many chemists have been curious about the heat effects that accompany chemical reactions. In the early 1780s the French chemist Lavoisier measured the heat given off by a guinea pig. He kept the animal in an enclosed container so that its body heat would melt ice. From the amount of ice melted, he calculated the heat produced by the animal.

The apparatus used to contain the guinea pig and measure its body heat was an ice calorimeter. It was forerunner of a family of devices used to measure heat in chemical reactions. In all calorimeters a reaction is allowed to take place inside an insulated container. The heat given off by the process is transferred (with as little loss as possible) to some other material. The heat can then be calculated for the change in temperature.

In this lab our calorimeter is made from Styrofoam cups. The initial temperature of the solvent and the final temperature of the solution are measured. Using the change in temperature, the specific heat capacity of water, and the total volume of water involved in the cup, the heat given off can be calculated. There are some obvious sources of error in this type of experiment. Heat form the reaction will also go into heating the cup. Some will be lost to the environment because the cup is not completely closed. If the substances are not completely mixed, the temperature measurements will not be accurate.

Make-up Questions

Purpose: To develop a classification scheme for types of mixtures.

1. For each of the unknowns record the color, clearness, if there is settling, and if the Tyndall effect is present.

2. The mixtures were then filtered.

3. Record the color, clearness, if there is settling, and if the Tyndall effect is present for each of the filtered unknowns.

 Make-up Questions

 Make-up Questions